1. Field of the Invention
The present invention relates to a method for the sizing of paper surfaces by use of a statistical copolymer of maleic acid anhydride and dicyclopentadiene and to the reaction products of these copolymers.
2. Description of the Prior Art
It is generally known to size paper in the pulp form by use of rosin soaps and aluminum ions. Besides of the known sizing agents based on rosin derivatives other solutions or dispersions of polymer compositions have been utilized for the sizing of paper. The advantage of such synthetic agents arises from the fact that they can also be brought to the already finished paper surface, while a normal resin glue with aluminum ions precipitates on the paper fibers.
The utilization of synthetic polymer sizing agents allows paper sizing without addition of metal salts. As examples of such sizing agents are solutions or dispersions of statistical copolymers of unsaturated carboxylic acids and their derivatives with specific ethylenic unsaturated compounds. The degree of sizing of these, state of the art copolymer-sized papers, is not always in accord with the technical requirements, as for example in the sizing of presized paper pulp.
It is known from DT-OS 1621693 that copolymers containing succinic acid imide groups can be used for the sizing of paper surfaces, wherein said copolymers contain vinylogous compounds as comonomers. As a possible vinylogous compound is mentioned, among others dicyclopentadiene. In order to make these copolymers soluble for the paper sizing, they have to be reacted with ammonia, bases or amines. This treatment with base, causes the formation of a variety of undesired derivatives becasue of the imide group content of the copolymer.
By the above mentioned method, it is necessary in order to form the imide groups, either to transform maleic acid anhydride into maleic acid imide or to form the imide groups from a copolymer composed of maleic acid anhydride and vinylogous compounds. Because of industrial interest it is desirable to simplify the preparation of the paper sizing agents containing copolymers and also based on a need for better reproducibility, to keep the number of the above mentioned derivatives obtained upon solution, under strict control.